A fuel cell system is an electric power generating system for converting chemical energy of a fuel directly into electrical energy. Generally, the fuel cell system includes a fuel cell stack for generating electrical energy. A fuel supply device supplies a fuel (i.e. hydrogen) to the fuel cell stack. An air supply device supplies oxygen in air, which is an oxidizing agent required for an electrochemical reaction, to the fuel cell stack. A heat and water management device radiates reaction heat of the fuel cell stack to outside of the system and controls an operating temperature of the fuel cell stack. The fuel cell system generates electricity as a result of the electrochemical reaction of oxygen included in the air and hydrogen which is the fuel, and discharges heat and water as by-products of the reaction.
The fuel cell stack applied to a fuel cell vehicle includes a plurality of unit cells sequentially arranged. Each unit cell includes a membrane-electrode assembly (MEA) disposed at the innermost part thereof. The membrane-electrode assembly includes an electrolyte membrane capable of transporting hydrogen ions (protons), and catalyst layers such as a cathode and an anode, which are coated on both sides of the electrolyte membrane such that hydrogen and oxygen can react with each other. In addition, a gas diffusion layer (GDL) is disposed at an exterior portion of the MEA, i.e. at the exterior portion in which the cathode and the anode are positioned. In addition, a separator, in which flow fields are formed to supply the fuel and the air to the cathode and the anode and to discharge water generated by the reaction, is positioned at an exterior of the GDL. In addition, an end plate is positioned at both ends of the stack so as to support the stacked cells.
In the stack, hydrogen and oxygen are ionized by chemical reactions by respective catalyst layers, such that an oxidation reaction generating hydrogen ions and electrons occurs at an electrode to which the hydrogen is supplied, and a reduction reaction generating water occurs at an electrode to which oxygen is supplied. Generally, a catalyst including a platinum catalyst and a cocatalyst, such as Ru, Co, and Cu, with a catalyst support made of a carbon material is usually used as an electrode catalyst in the fuel cell. That is, hydrogen is supplied to the anode (referred to as an oxidation electrode), and oxygen, i.e. air, is supplied to the cathode (referred to as a reduction electrode). Accordingly, the hydrogen supplied to the anode is resolved into hydrogen ions (protons) “H+” and electrons “e−” by the catalysts of the electrode layers configured at both sides of an electrolyte membrane. Then, among the hydrogen ions and electrons, only the hydrogen ions (protons) “H+” are selectively transferred to the cathode through an electrolyte membrane, which is a positive ion exchange membrane. Simultaneously with this, the electrons “e−” are transferred to the cathode through a gas diffusion layer, which is a conductor, and a separator. In the cathode, the hydrogen ions supplied through the electrolyte membrane and the electrons supplied through the separator meets oxygen in air, which is supplied to the cathode by an air supply device, and produces a reaction to generate water. The movement of hydrogen ions caused at this time causes flow of electrons through an external conducting wire to generate current, wherein heat in addition to water is incidentally generated.
In general, the stack is housed by an enclosure in order to physically protect the stack in which a high voltage is generated. However, because of moisture introduction through a crevice of the enclosure, moisture condensation by a temperature difference between inner air and outer air of the enclosure due to an exothermic reaction of the stack, leak of some moisture from the stack during operating of the stack, or the like, the components of the stack in the enclosure may be corroded, and an insulation resistance may be deteriorated.
The information disclosed in this Background section is only for enhancement of understanding of the general background of the disclosure and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.